Mr Kinghorn, 71, who made half a billion dollars in the controversial float of his company Rams Home Loans, in late 2007, was being grilled about his knowledge of Cascade Coal.

Mr Kinghorn was part of a syndicate of extraordinarily wealthy businessmen, dubbed the ''magnificent seven'', who invested in Cascade Coal which is now facing allegations it was corruptly awarded a coal exploration licence in 2009 by the then mining minister Ian Macdonald.

The family of Labor powerbroker Eddie Obeid also stands accused of using inside information provided to them by Mr Macdonald, to demand a 25 per cent stake in Cascade.

Mr Kinghorn was one of five directors of the publicly listed company White Energy who were also investors in Cascade Coal when White Energy offered to buy Cascade for $500 million in late 2010.

The remaining three ''independent directors'' were given the job of deciding whether the deal was a good one for White shareholders.

The inquiry has heard that independent director Graham Cubbin was concerned about rumours that the Obeids were involved in Cascade, which might lead the incoming Liberal government to cancel Cascade's licence. This would mean the $500 million acquisition would be worthless.

''I'm going to suggest to you that you didn't tell the ordinary shareholders of White Energy because you were deliberately withholding that information, do you accept that?'' Mr Kinghorn was asked. ''No, I call that under the heading of tripe,'' he snapped in reply.

The inquiry has heard that White Energy directors Mr Kinghorn, Travers Duncan, John Atkinson, John McGuigan and Brian Flannery each stood to make between $50 million and $60 million from the sale of their company Cascade to White Energy.

Mr Kinghorn has been played a number of intercepted phone calls in which he was heard belittling Mr Cubbin. In an intercepted call to his friend Greg Jones, recorded in April last year, Mr Kinghorn was heard saying about Mr Cubbin: ''We just got to get there first … then we'll chop the arsehole's head off.''

The commission has heard that the White Energy purchase of Cascade did not take place because of concerns that the stock exchange was asking questions which might have revealed the Obeids' involvement.

Under the Corporations Act, a director must act in the best interests of the company and for a proper purpose. A breach of this duty may attract criminal penalties.

The inquiry continues.

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